> *** Remember that although the opal_hwloc_topology global variable will
always be available, ##IT MAY BE NULL## on platforms where hwloc was
compiled out / not supported. Therefore, you MUST protect access to hwloc
API calls with #if OPAL_HAVE_HWLOC! See the original RFC text below.

Oops! Ralph just reminded me that this was slightly inaccurate.

If hwloc is not present, then the global variable opal_hwloc_topology won't
be present at all (because its corresponding hwloc type won't be available).
Hence, the example in the original RFC isn't quite right: